Probe unit substrate

ABSTRACT

A ceramic substrate has, on its surface, a multilayer wiring division, on which micro cantilever type probes are fixed. The multilayer wiring division has the first conductor layer, which includes through-hole junction pads, flatness improvement rings surrounding the through-hole junction pads and a grounding region further surrounding the flatness improvement rings. Since the flatness improvement rings are located around the through-hole junction pads, the surface of the first insulating layer, which is located above the first conductor layer, is free from severe undulation even near the through-hole junction pads. Accordingly, the multilayer wiring division has less irregularity in shape as a whole, and thus the probe mounting pads on the surface of the second insulating layer do not slope but keep almost horizontal. The probe unit substrate according to the invention has an advantage of less surface undulation and having non-sloping probe mounting pads without using a complicated manufacturing process.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a Divisional Application of U.S. applicationSer. No. 12/005,488 filed Dec. 27, 2007, which is incorporated herein byreference.

BACKGROUND OF THE INVENTION

The present invention relates to a probe unit substrate having a featureof planarization or leveling of probe mounting pads.

In this specification, the phrase “probe unit” signifies a unit havingplural probes for testing electronic parts or electrical parts, and thusit corresponds to, for example, a probe card used for testing anelectrical circuit on a semiconductor wafer or a probe unit used fortesting a liquid crystal display. Further, the phrase “probe unitsubstrate” signifies a substrate for the probe unit, which has aninternal wiring and is possible to support plural probes.

FIG. 11 is an enlarged sectional view illustrating a part of aconventional probe unit substrate. A ceramic substrate 10 has a surface,on which the first conductor layer 12 is formed in a predeterminedpattern. Above the first conductor layer 12 are formed the firstinsulating layer 14, the second conductor layer 16, and the secondinsulating layer 18 in order. On the surface of the second insulatinglayer 18 are formed a number of probe mounting pads 20. Micro cantilevertype probes 22 are fixed to the respective probe mounting pads 20. Thefirst conductor layer 12 is formed to be a predetermined pattern, andincludes through-hole Junction pads 24 and a grounding region 26. Theceramic substrate 10 is formed with through-holes 28, and innerconductors of the through-holes 28 are connected with the through-holejunction pads 24. The through-hole junction pad 24 is prepared for thepurpose of absorbing a positional displacement, which might be caused bythermal contraction of the through-hole conductor of the ceramicsubstrate 10. The through-hole junction pads 24 are connected to thesecond conductor layer 16.

A clearance between the through-hole junction pad 24 and a groundingregion 26 is filled with the first insulating layer 14 depositedtherein. Accordingly, the surface of the first insulating layer 14becomes not flat but shows undulation. Such undulation spreads to thesecond conductor layer 16 and the second insulating layer 18. Besides,if the second conductor layer 16 is formed in a predetermined pattern,other undulation resulting from the pattern is also added. As a result,undulation appears on the surface of the second insulating layer 18. Ifthe probe mounting pad 20 rests on such an uneven surface of the secondinsulating layer 18, the surface of the probe mounting pad 20 would bein danger of being non-flat or being inclined from the horizontalcondition even with flatness. Further, if the micro cantilever typeprobes 22 are fixed to the respective such probe mounting pads 20, itcould lead to variation in heights of tips 30 of a number of probes 22.

The surface undulation of the first insulating layer 14 will bealleviated if the clearance between the through-hole junction pad 24 andthe grounding region 26 is reduced. However, there is a restriction inreduction of the clearance, as will be described below. FIG. 12A is aplan view illustrating a pattern of the first conductor layer 12 aroundthe through-hole junction pad 24. The clearance 32 (a space having noconductor layer) is formed around the through-hole junction pad 24, andthus the through-hole junction pad 24 is separated from the groundingregion 26 with a distance d. The distance d is a hundred micrometers,for example.

Since the surface undulation of the first insulating layer 14 is causedby existence of the clearance 32, it would be possible to alleviate suchundulation if the distance d is reduced. That is, as shown in FIG. 12B,it might be possible to reduce the distance d down to twenty-fivemicrometers for example. However, if the distance d is reduced, anotherproblem occurs as described below. As shown in FIG. 12C, when a foreignparticle 34 gets stuck in the clearance 32, there is a risk of shortcircuit between the through-hole junction pad 24 and the groundingregion 26. Therefore, it is not very preferable to reduce the distanced. Much the same is true in the case of short circuit caused by anywrong pattern instead of the foreign particle 34.

FIG. 13 is a sectional view illustrating in a magnified form a part ofanother structure of the conventional probe unit substrate. In thisprobe unit substrate, a multilayer wiring division 42 is composed of thefirst conductor layer 12, the first insulating layer 14, the secondconductor layer 16, the second insulating layer 18, the third conductorlayer 54, the third insulating layer 56, the fourth conductor layer 58,the fourth insulating layer 60, the fifth conductor layer 62 and thefifth insulating layer 64. On the surface of the fifth insulating layer64 are formed a number of probe mounting pads 20. This conventionalstructure brings, as well as the conventional structure as shown in FIG.11, irregularity to the surface of the first insulating layer 14 causedby the fact that the first insulating layer 14 is deposited in theclearance between the through-hole junction pad 24 and the groundingregion 26. In addition, for example, the wiring patterns formed in thesecond conductor layer 16 and the fourth conductor layer 58 bring theirregularity to the surfaces of the insulating layers 18 and 60 disposedabove the conductor layers 16 and 58. These irregularities spill overinto the uppermost surface of the fifth insulating layer 64 so that thesurfaces of the probe mounting pads 20 would not be flat or would beinclined from the horizontal condition no matter how flat the surfaceis.

By the way, the technique regarding planarization of a multilayer wiringsubstrate is known as described below. Concerning the technique forfixing a probe to a conductor layer (which corresponds to the probemounting pad) formed on the uppermost layer of the multilayer wiringsubstrate, an improvement in the surface flatness of the multilayerwiring substrate is disclosed in Japanese Patent Publication No.2006-210473 A (the first publication).

In the first publication, a covering resin layer having through-holes isformed on an insulating base, and the through-holes are filled withconductor layers. Accordingly, the height of the surface of the coveringresin layer is almost the same as the heights of the surfaces of theconductor layers, resulting in no irregularity. Then, an insulatingresin layer and a wiring conductor layer can be formed above acombination of the above-described covering resin layer and theconductor layers. Accordingly, the surface irregularity of themultilayer wiring substrate is alleviated, and a conductor layer isformed on the surface of the multilayer wiring substrate and a number ofprobes are fixed to the conductor layer without variation in heights ofthe tips of the probes.

According to the above-described technique disclosed in the firstpublication, the surface irregularity of the multilayer wiring substrateis reduced, but the manufacturing process will be complicated to form “acovering resin layer having through-holes”. According to the firstpublication, formation of the through-hole in the covering resin layerrequires 1) oxygen plasma treatment on the top side of the coveringresin layer with the use of a metal layer as a mask, or 2) laserprocessing for removing a part of the covering resin layer to formthrough-holes.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a probe unitsubstrate in which the surface irregularity is alleviated without acomplicated manufacturing process so that the probe mounting padsneither undulate nor slope. The probe unit substrate according to thepresent invention is characterized in formation of flatness improvementrings or planarization patterns in the multilayer wiring division sothat the probe mounting pads keep the flat and horizontal conditions.The probe unit substrate according to the first aspect of the presentinvention has flatness improvement rings, and thus comprises: (a) anelectrical insulating substrate having a surface; (b) a first conductorlayer formed on the surface of the substrate, the first conductor layerincluding: first conductor patterns; flatness improvement ringssurrounding the first conductor patterns with first clearancestherebetween; and a second conductor pattern surrounding the flatnessimprovement rings with second clearances therebetween; (c) a firstinsulating layer covering over the first conductor layer; (d) at leastone other conductor layer formed above the first insulating layer, andat least one other insulating layer covering over the other conductorlayer; and (e) probe mounting pads formed on a surface of an uppermostinsulating layer of the at least one other insulating layer.

It should be noted, in the present specification, that the words “above”and “beneath” signify the directions described below. The word “above”signifies a direction from the electrical insulating substrate towardthe probe mounting pads, and the word “beneath” signifies the oppositedirection. Therefore, the words “above” and “beneath” have no connectionto the posture of the probe unit substrate and its components againstthe gravity.

The probe unit substrate according to the second aspect of the presentinvention has planarization patterns, and thus comprises: (a) anelectrical insulating substrate having a surface; (b) a first conductorlayer formed on the surface of the substrate; (c) a first insulatinglayer covering over the first conductor layer; (d) at least one otherconductor layer formed above the first insulating layer, and at leastone other insulating layer covering over the other conductor layer; and(e) probe mounting pads formed on a surface of an uppermost insulatinglayer of the at least one other insulating layer. Further, the probeunit substrate according to the second aspect has a feature in which: atleast one of the at least one other conductor layer has a conductorpattern and planarization patterns insulated from the conductor pattern;each of the planarization patterns has a plane size greater than theprobe mounting pad; and the planarization patterns are located beneaththe probe mounting pads.

The probe unit substrate according to the third aspect of the presentinvention has both flatness improvement rings and planarizationpatterns, and thus comprises: (a) an electrical insulating substratehaving a surface; (b) a first conductor layer formed on the surface ofthe substrate, the first conductor layer including: first conductorpatterns; flatness improvement rings surrounding the first conductorpatterns with first clearances therebetween; and a second conductorpattern surrounding the flatness improvement rings with secondclearances therebetween; (c) a first insulating layer covering over thefirst conductor layer; (d) at least one other conductor layer formedabove the first insulating layer, and at least one other insulatinglayer covering over the other conductor layer; and (e) probe mountingpads formed on a surface of an uppermost insulating layer of the atleast one other insulating layer. Further, the probe unit substrateaccording to the third aspect has a feature in which: at least one ofthe at least one other conductor layer has a third conductor pattern andplanarization patterns insulated from the third conductor pattern; eachof the planarization patterns has a plane size greater than the probemounting pad; and the planarization patterns are located beneath theprobe mounting pads.

The probe unit substrate according the present invention has anadvantage that the surface irregularity of the multilayer wiringdivision is alleviated so that the probe mounting pads on its surfaceneither undulate nor slope because of the formation of the flatnessimprovement rings or the planarization patterns as described above.Therefore, there is no variation in heights of the tips of the probesthat are fixed to a number of the probe mounting pads respectively

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an elevation view of the probe card provided with the probeunit substrate according to the present invention;

FIG. 2 is a side sectional view of a part of the probe unit substrateaccording to the first embodiment of the present invention;

FIGS. 3A and 3B are plan views illustrating a pattern near thethrough-hole junction pad of the first conductor layer in the firstembodiment of the present invention;

FIG. 4 is a side sectional view of a part of the probe unit substrateaccording to the second embodiment of the present invention;

FIG. 5 is a side sectional view of a part of the probe unit substrateaccording to the third embodiment of the present invention;

FIG. 6 is a side sectional view of a part of the probe unit substrateaccording to the fourth embodiment of the present invention;

FIG. 7 is a fragmentary plan view of the probe card shown in FIG. 1 asviewed from the bottom of FIG. 1;

FIG. 8 is a fragmentary plan view illustrating a modified planar shapeof the planarization pattern;

FIG. 9 is a fragmentary plan view illustrating another modified planarshape of the planarization pattern;

FIG. 10 is a sectional view taken along the line A-A in FIG. 9;

FIG. 11 is a sectional view illustrating a part of the conventionalprobe unit substrate in a magnified form;

FIGS. 12A, 12B and 12C are plan views illustrating a pattern around thethrough-hole junction pad of the first conductor layer in the prior art;and

FIG. 13 is a sectional view illustrating a part of another conventionalprobe unit substrate in a magnified form.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention will be described in detail belowwith reference to the drawings. FIG. 1 is an elevation view of the probecard provided with a probe unit substrate according to the presentinvention. A probe unit substrate 38 is fixed to one side of a wiringsubstrate 36, and a reinforcing plate 40 is fixed to the other side ofthe wiring substrate 36. The probe unit substrate 38 is equipped with aceramic substrate 10 and a multilayer wiring division 42. On the surfaceof the ceramic substrate 10 is formed the multilayer wiring division 42made of thin films, on the surface of which are formed a number of probemounting pads. Micro cantilever type probes 22 are fixed to therespective probe mounting pads.

FIG. 2 is a side sectional view of a part of the probe unit substrateaccording to the first embodiment of the present invention. On theceramic substrate 10 is formed the multilayer wiring division 42, onwhich the micro cantilever type probes 22 are fixed. The ceramicsubstrate 10 corresponds to the electrical insulating substrate in thepresent invention. The multilayer wiring division 42 consists of thefirst conductor layer 12, the first insulating layer 14, the secondconductor layer 16 and the second insulating layer 18. The firstconductor layer 12 includes through-hole junction pads 24, flatnessimprovement rings 48 that surround the through-hole junction pads 24,and a grounding region 26 that further surrounds the flatnessimprovement rings 48. The ceramic substrate 10 is formed withthrough-holes 28. Conductors buried inside the through-holes 28 areconnected with the through-hole junction pads 24 respectively. Thethrough-hole junction pad 24 is formed for the purpose of absorbing apositional displacement that might be caused by heat shrinkage of thethrough-hole conductor in the ceramic substrate 10. The through-holejunction pad 24 is connected, via the conductor inside the through-hole28, to a wiring on the other side of the ceramic substrate 10. On theother hand, the through-hole junction pad 24 is connected to the secondconductor layer 16. On the surface of the second insulating layer 18 areformed a number of probe mounting pads 20. On the probe mounting pad 20is fixed the root of a probe 22. As the flatness improvement ring 48exists around the through-hole junction pad 24, the surface of the firstinsulating layer 14 never billows near the through-hole junction pad 24.Accordingly, the multilayer wiring division 42 has smaller undulation asa whole, and thus the probe mounting pad 20 on the second insulatinglayer 18 never undulates. Further, the probe mounting pad 20 neverslopes but keeps horizontal. Therefore, the probes 22 that are fixed tothe probe mounting pads 20 have no variation in heights of their tips30.

FIG. 3A is a plan view illustrating a pattern near the through-holejunction pad 24 of the first conductor layer 12 (see FIG. 2). The centeron the backside of the through-hole junction pad 24 is connected to thethrough-hole 28. Around the through-hole junction pad 24 is formed theflatness improvement ring 48 with the first clearance 50 therebetween.Further, around the flatness improvement ring 48 is formed a groundingregion 26 with the second clearance 52 therebetween. The through-holejunction pad 24 corresponds to the first conductor pattern in thepresent invention, and the grounding region 26 corresponds to the secondconductor pattern in the present invention. The flatness improvementring 48 surrounds the through-hole junction pad 24 with the firstclearance 50 therebetween, and further the grounding region 26 surroundsthe flatness improvement ring 48 with the second clearance 52therebetween. The distance d1 of the first clearance 50 is 25micrometers for example, and the distance d2 of the second clearance is25 micrometers for example. The width of the flatness improvement ring48 is 520 micrometers for example. As the distances d1 and d2 aresmaller than the clearance d in the prior art (see FIG. 12A), thesurface drop of the first insulating layer 14 (see FIG. 2) near thefirst clearance 50 and the second clearance 52 is alleviated, so thatthe surface undulation of the first insulating layer 14 is reduced.

Now, the risk of short circuit will be described. As shown in FIG. 3B,it is assumed that a foreign particle 34 gets stuck in the firstclearance 50. Since the distance of the first clearance 50 is set small,if the foreign particle 34 gets stuck therein the short circuit mightoccur between the through-hole junction pad 24 and the flatnessimprovement ring 48. The through-hole junction pad 24, however, nevershort-circuits with the grounding region 26 because the flatnessimprovement ring 48 is insulated from the grounding region 26. Much thesame is true if the foreign particle gets stuck in the second clearance52 instead of in the first clearance 50. Nevertheless, if foreignparticles get stuck in both of the first clearance 50 and the secondclearance 52, there would be a risk of the short circuit between thethrough-hole junction pad 24 and the grounding region 26, a possibilityof such a situation being extremely low. Accordingly, comparing to theconventional pattern shown in FIG. 12B, the risk of short circuit isremarkably reduced.

FIG. 4 is a side sectional view of a part of the probe unit substrateaccording to the second embodiment of the present invention. Thisembodiment has no above-described flatness improvement ring butplanarization patterns. The multilayer wiring division 42 in thisembodiment consists of the first conductor layer 12, the firstinsulating layer 14, the second conductor layer 16, the secondinsulating layer 18, the third conductor layer 54, the third insulatinglayer 56, the fourth conductor layer 58, the fourth insulating layer 60,the fifth conductor layer 62, and the fifth insulating layer 64 On thesurface of the fifth insulating layer 64 are formed a number of probemounting pads 20.

The first conductor layer 12 includes the through-hole junction pads 24and the grounding region 26 that surrounds the through-hole junctionpads 24, but has no flatness improvement ring. The second conductorlayer 16, the third conductor layer 54 and the fourth conductor layer 58are wiring layers. On the other hand, the fifth conductor layer 62 is agrounding layer. The second conductor layer 16 includes planarizationpatterns 66 and a predetermined conductor pattern 67. The predeterminedconductor pattern 67 corresponds to the third conductor pattern in thepresent invention. The fourth conductor layer 58 also includesplanarization patterns 68 and a predetermined conductor pattern 69. Thepredetermined conductor pattern 69 also corresponds to the thirdconductor pattern in the present invention. The planarization patterns66 and 68 are located beneath the probe mounting pads 20. The planarsizes of these planarization patterns 66 and 68 are larger than theplanar size of the probe mounting pad 20. Further, the planar size ofthe lower planarization pattern 66 is larger than the planar size of theupper planarization pattern 68. Namely, comparing these planar sizes,there is a relationship that the probe mounting pad 20 is smaller thanthe planarization pattern 68, which is further smaller than theplanarization pattern 66. For example, the probe mounting pad 20 is 120micrometers square in planar size, the planarization pattern 68 is 150micrometers square, and the planarization pattern 66 is 180 micrometerssquare. The planarization patterns 66 and 68 are intended to erase theboundary (which is the planar boundary between the conductor layer andthe insulating layer) beneath the probe mounting pads 20. Theplanarization patterns 66 and 68 reduce, in the vicinity of theplanarization patterns 66 and 68, the surface undulation of the secondinsulating layer 18 located above the planarization pattern 66 and thesurface undulation of the fourth insulating layer 60 located above theplanarization pattern 68. As a result, the surface undulation of thefifth insulating layer 64 is reduced in the vicinity of the probemounting pads 20. Accordingly, the probe mounting pads 20 never undulateand keep almost horizontal. Therefore, the probes 22, which are fixed tosuch probe mounting pads 22, have no variation in heights of their tips30. The planarization patterns 66 and 68 are preferably electricallyconnected with different patterns made of respective identical conductorlayers, noting that it does not matter what kind of an electricalpotential for the different pattern.

FIG. 5 is a side sectional view of a part of the probe unit substrateaccording to the third embodiment of the present invention. Thisembodiment is similar to the second embodiment shown in FIG. 4, but itdiffers from the second embodiment in the point that the third conductorlayer 54 also includes planarization patterns 70 and the fifth conductorlayer 62 also includes planarization patterns 72. These planarizationpatterns 70 and 72 are also located beneath the probe mounting pads 20and have the planar sizes larger than the planar size of the probemounting pads 20. In the third embodiment, all of the conductor layers16, 54, 58 and 62 ranging from the second conductor layer 16 to thefifth conductor layer 62 include planarization patterns 66, 70, 68 and72. The planar sizes of these planarization patterns become larger whenlocated lower, that is, there is a relationship in size that the probemounting pad 20 is smaller than the planarization pattern 72, which issmaller than the planarization pattern 68, which is smaller than theplanarization pattern 70, which is smaller than the planarizationpattern 66. For example, the probe mounting pad 20 is 120 micrometerssquare in planar size, the planarization pattern 72 is 135 micrometerssquare, the planarization pattern 68 is 150 micrometers square, theplanarization pattern 70 is 165 micrometers square, and theplanarization pattern 66 is 180 micrometers square.

FIG. 6 is a side sectional view of a part of the probe unit substrateaccording to the fourth embodiment of the present invention. Thisembodiment is similar to the second embodiment shown in FIG. 4, butfurther includes the flatness improvement rings 48 shown in FIG. 2.Namely, in FIG. 6, the first conductor layer 12 includes thethrough-hole junction pads 24, the flatness improvement rings 48 thatsurround the through-hole junction pads 24 and the grounding region 26that further surrounds the flatness improvement rings 48. The secondconductor layer 16 includes the planarization patterns 66, and thefourth conductor layer 58 includes the planarization patterns 68. Thisembodiment has advantageously a combination of the planarization effectof the flatness improvement rings 48 and the planarization effect of theplanarization patterns 66 and 68.

Next, the planar shape of the planarization pattern will be described.FIG. 7 is a fragmentary plan view of the probe card shown in FIG. 1 asviewed from the bottom of FIG. 1, the probe card being equipped with theprobe unit substrate 38, which has the planarization patterns shown inFIG. 5. A number of probes 22 are mounted on the surface of the probeunit substrate 38. Imaginary scribe lines 44 for IC chips, which can bemeasured with the probe card, are shown by dashed lines. Theplanarization patterns 72 shown in FIG. 5 are formed inside themultilayer wiring division of the probe unit substrate 38. The probemounting pads 20 are located above the planarization patterns 72. Theplanarization patterns 72 may be prepared one by one for the respectiveprobe mounting pads 20, but in this embodiment one planarization pattern72 is prepared for plural probe mounting pads 20, noting that the oneplanarization pattern 72 may be associated with any number of the probemounting pads 20.

FIG. 8 is a fragmentary plan view illustrating a modified planar shapeof the planarization pattern. This embodiment differs from theembodiment shown in FIG. 7 in the relationship between the planarizationpatterns 72 and the probe mounting pads 20. One planarization pattern 72is associated with two probe mounting pads 20.

FIG. 9 is a fragmentary plan view illustrating another modified planarshape of the planarization pattern. The uppermost layer of themultilayer wiring division is the fifth insulating layer, and a numberof probe mounting pads 20 are formed thereon. On the probe mounting pads20 are fixed the probes 22. The fifth conductor layer 62 is locatedbeneath the fifth insulating layer. The fifth conductor layer 62 (shownby hatching running from upper right to lower left) is a groundinglayer, and includes a grounding region 74 and the planarization patterns72, which are located beneath the probe mounting pads 20. If theconductor layer that is located beneath and close to the probe mountingpads 20 is the grounding layer, the grounding layer may have only asolid pattern, which covers almost all area. In this embodiment,however, in consideration of easiness of repairing a short circuit placeas described later, the conductor layer includes the planarizationpatterns 72. The planarization patterns 72 are electrically connectedwith the grounding region 74, and compose a part of the grounding layer.The probe mounting pads 20 in this embodiment each has an elongateshape, and these probe mounting pads 20 are divided into groups, eachgroup including plural pads. The planarization patterns 72, each ofwhich may be associated with plural probe mounting pads belonging to onegroup, are connected to each other via narrow joints 76. Theplanarization patterns 72 are further connected to the grounding region74 via other narrow joints 78. The widths of the narrow joints 76 and 78are 50 to 100 micrometers for example.

FIG. 10 is a sectional view taken along the line A-A in FIG. 9. It isassumed that a short circuit place 80 (see also FIG. 9) has occurred forsome reason between the probe mounting pad 20 and the planarizationpattern 72. Since the planarization pattern 72 is at the groundpotential as shown in FIG. 9, the above-described short circuitunfavorably brings the probe mounting pad 20 to the ground potential, sothat the pad 20 can not feed, to the probe 22, an electrical signal forwafer testing. Then, it is necessary to repair the short circuit place80. However, a repairing process by cutting the short circuit place perse would raise the risk of irregularity, which may be caused by therepairing process just beneath the probe mounting pad 20, and thus sucha repairing process is not preferable. Therefore, in this embodiment, asshown in FIG. 9, the two joints 76 may be cut at the line B-B and theline C-C. When the joints 76 are cut, any irregularity would not occurjust beneath the probe mounting pad 20. Even if any irregularity occursafter the repairing process, it would not affect the flatness of theprobe mounting pad 20.

1. A probe unit substrate comprising: (a) an electrical insulatingsubstrate having a surface; (b) a first conductor layer formed on thesurface of the substrate, the first conductor layer including: firstconductor patterns; flatness improvement rings surrounding the firstconductor patterns with first clearances therebetween; and a secondconductor pattern surrounding the flatness improvement rings with secondclearances therebetween; (c) a first insulating layer covering over thefirst conductor layer; (d) at least one other conductor layer formedabove the first insulating layer, and at least one other insulatinglayer covering over the other conductor layer; and (e) probe mountingpads formed on a surface of an uppermost insulating layer of the atleast one other insulating layer.
 2. The probe unit substrate accordingto claim 1, wherein the first conductor pattern of the first conductorlayer is a through-hole junction pad, which is connected via athrough-hole conductor to a wiring on another side of the electricalinsulating substrate.
 3. The probe unit substrate according to claim 1,wherein the second conductor pattern of the first conductor layer is agrounding region.
 4. The probe unit substrate according to claim 1,wherein the first clearance between the flatness improvement ring andthe first conductor pattern has a distance of 25 micrometers, and thesecond clearance between the flatness improvement ring and the secondconductor pattern has a distance of 25 micrometers.
 5. The probe unitsubstrate according to claim 1, wherein the probe unit further comprisesmicro cantilever type probes each having a root, which is fixed to oneof the probe mounting pads.